Pharmaceutical, biotechnology, or genomics companies use DNA analysis systems for target identification and drug screening in pharmaceutical drug discovery. In many of these systems, biomolecules (e.g., DNA, RNA, cDNA, proteins) labeled with various dyes bind to chips that offer different molecular probe counterparts for binding in different locations of the chip. An optical scanner is then used to read the fluorescence of these resultant surface bound molecules under illumination with suitable (most often laser) light. Another type of detection for arrays involves the use of multiple electrode elements patterned with various biological molecules on the surface to detect analytes labeled with electrochemically active probes. A third array method operates by optical detection of semiconductor nanopartices attached to biological molecules.
Another mode of scanning is presented in U.S. Pat. No. 5,633,724. As with the other modes of detection noted above, the method taught in the patent requires that probes be attached to the biological molecules of interest. In the case of the '724 patent, fluorescent labeling is used. In contrast to the aforementioned fluorescence-based detection technique, however, this approach employs evanescent excitation of tags or labels instead of direct illumination of the same.
Evanescence involves a situation where incident light is totally reflected off of a surface, but the electromagnetic field component penetrates a short distance (tens of nanometers) into an adjacent medium
While many array-based studies of bioaffinity interactions employ fluorescently labeled biopolymers, there is a recognized need for the continued development of sensitive analytical methods that can be used to detect bioaffinity interactions in biological samples without the need of molecular labels or tags. This is especially true for the case of protein-protein interactions, where labeling is difficult and can interfere with protein function.
SPR imaging is used today to detect the presence of a biopolymer on a chemically modified gold surface by the change in the local index of refraction that occurs upon adsorption. Conventional implementations of SPR analysis involve only one element (one region over which detection is measured) or 3–5 elements in a parallel arrangement at most. However, such systems are not amenable to carrying out high-throughput methodologies.